"Teenager" redirects here. For this article is about one of the stages of human development. For the punk rock band, see The Adolescents.

Adolescence (Latinadolescentia, from adolescere, to grow up) is the period of psychological and social transition between childhoodd and adulthood (gender-specific, manhood or womanhood). In common usage in western, English language countries, "adolescent" and "teenager" may be considered synonyms (though it should be noted that the term 'teenager' is an artifact of the English counting system, not something that occurs in most languages), though the exact endpoints of each category don't always coincide depending on the definition of "adolescent" being used. Adolescence is the transitional stage of human development in which a juvenile matures into an adult. This transition involves biological (i.e. pubertal), social, and psychological changes, though the biological ones are the easiest to measure objectively.

"Adolescence" is a modern cultural and social phenomenon and therefore its end points are not easily tied to physical milestones and historically this stage of development has not existed in its current form. The time is identified with dramatic changes in the body, along with developments in a person's psychology and academic career. In the onset of adolescence, children usually complete elementary school and enter secondary education, such as middle school or high school. A person between early childhood and the teenage years is sometimes referred to as a pre-teen or tween.

The ages of adolescence vary by culture. The World Health Organization (WHO) defines adolescence as the period of life between 10 and 19 years of age. In contrast, in the United States, adolescence is generally considered to begin somewhere between ages 12 and 14, and end at 19 or 20. As distinct from the varied interpretations of who is considered an "adolescent", the word "teenager" is more easily defined: it describes a person who is thirteen to nineteen years of age.

During this period of life, most children go through the physical stages of puberty which, in recent times, has begun between the ages of nine and thirteen, while historically began much later. (See Puberty below)

Most cultures regard people as becoming adults at various ages of the teenage years. (See Social and cultural below)

Puberty

Puberty is the stage of the human lifespan in which a child develops secondary sex characteristics as his or her hormonal balance shifts strongly towards an adult state. This is triggered by the pituitary gland, which secretes a surge of hormones into the blood stream and begins the rapid maturation of the gonads: the girl's ovaries and the boy's testicles. Girls tend to enter puberty approximately a year earlier than boys.

The onset of puberty in girls especially appears to be related to body fat percentage. In most Western countries, the average age of menarche fell, in a secular trend, over the last century. There are numerous theories as to why this is including improved nutrition, increased caloric intake, increased artificial hormones present in meats, other preservatives and chemicals used in the modern processing of foods, and decreased melatonin levels due to the increased exposure to and prevalence of (artificial) lights such as are emitted from televisions, nightlights, and computer monitors.

Some theorists believe that analysis of data shows the age of onset of menarche to correlate to whether a girl lives with her natural father, a stepfather, or no father at all. Yet others propose a climatological connection and attribute the decreased average age of menarche in part to climate change or global warming. The debates regarding both of these theories are politically charged.

Historically this stage of development began much later, sometime between the ages of fourteen and eighteen, which allowed the child to mentally and emotionally mature more and brought them closer to the age of consent before reaching this physically and emotionally challenging developmental stage.

Preteens

The word preteen describes a child. The neologism tween has the same meaning, and isn't in general use as either a colloquial or scientific term. This word comes from the age being between that of a child and a teenager, and perhaps it has also been inspired by the first sounds of numeral twelve and the similarity to teen.

Preteens are increasingly a specifically targeted market segment by business, because they tend to maintain the preferences they develop at this age. Even mobile phones are targeted toward this group.

Preteen includes ages 8 to 12.
　

Teenagers

A teenager or teen is a person whose age is a number ending in "teen" in the English language: that is to say, someone from the age of thirteen to the age of nineteen. The word is of recent origin, only having appeared in the mid 20th century. Equivalent words in other languages may apply to a larger age bracket, including (at least some) preteens; e.g. tiener in Dutch officially from 12, colloquially from 10.

In Western culture, a distinct youth culture has developed. This culture is often distinctly different from the mainstream culture, sometimes in rebellion against it, and thus is often referred to as a subculture or counterculture.

Emerging adulthood

Some scholars have theorized a new stage of development, post-adolescence and pre-adulthood. Arnett (2000) calls this stage "emerging adulthood," and argues that it is characterized by "relative independence from social roles and from normative expectations. ... Emerging adulthood is a time of life when many different directions remain possible, when the scope of independent exploration of life's possibilities is greater for most people than it will be at any other period of the life course." (p.469). Arnett, notes, however, that this stage is situationally and culturally constructed (i.e., people in other countries may not experience this as a unique life stage.)

Psychology of adolescents

Physical maturation resulting from puberty leads to an interest in sexual activities, sometimes leading to teenage pregnancy. Increasingly, teenage sexual encounters do not occur in the context of a romantic relationship, but in an impersonal, merely sexual "hook up." The "impersonality of twenty-first-century adolescent sex victimizes girls" and "plenty of harm" is done to boys as well. As adolescents are not mentally or emotionally prepared to handle feelings and emotions that come with sex, nor financially able to support children, "early sexual activity - whether in or out of a romantic relationship - does far more harm than good."

The harm done to teenagers who engage in sexual activities is especially true for girls. In a 2003 study, 89% of girls reported feeling pressured by boys to have sex. Girls will often become intoxicated before engaging in sexual activities because it "numbs the experience for them, making it less embarrassing and less emotionally painful." A girl is "far more likely to feel used and abused after a typical" hook up. Boys are less likely to see sex as connected to an emotional relationship. However, by the time a young man is "in his early twenties, he will rely on his girlfriend or wife to be his primary emotional caregiver." If he can not establish an emotional relationship with a woman who views sex as connected to intimacy, then he is more likely to become depressed, commit suicide or die from illness.

At this age there is also a greater probability of drug and alcohol use, or mental health disorders such as schizophrenia, eating disorders such as anorexia, and depression. The unstable emotions or lack of emotional intelligence among some adolescents may also lead to youth crime.

Searching for a unique identity is another problem that adolescents face. Some, but not all, teenagers often challenge authority or the rules as a means to establish their individuality. They may crave adulthood and to find their place in the society.

G. Stanley Hall denoted this period as one of "Storm and Stress". Conflict at this developmental stage is normal and not unusual. Margaret Mead, on the other hand, attributed the behavior of adolescents to their culture. Piaget attributed this stage in development with greatly increased cognitive abilities, which can cause conflict as the individual has gained the cognitive ability to reason, dispute, and theorize on an adult level.

The information processing theory, on the other hand, does not see this as a qualitatively different stage, but rather just part of the uniformally gradual slope in gaining more experience. Another equally interesting view is the inventionist view, which states that adolescence is merely a creation of sociohistory. Especially important in this view are the sociohistorical circumstances at the beginning of the twentieth century, a time when legislation was enacted that ensured the dependency of youth and made their move into the economic sphere more manageable.

Positive Psychology is sometimes brought up when addressing adolescent psychology as well. In many groups, one encounters a surprising number of teens who are bored, unmotivated, and pessimistic about their future. A positive psychology styled approach attempts to start up their internal fires, help them develop the complex skills and dispositions necessary to take charge of their lives, to become socially competent, compassionate and psychologically vigorous adults. The article "Positive psychology and adolescent mental health: false promise or true breakthrough?", by Thomas M Kelly, discusses it more.

Social and cultural

In commerce, this generation is seen as an important target. Cellular phones, contemporary popular music, movies, television programs, sports, video games and clothes are heavily marketed and often popular amongst adolescents.

In the past (and still in some cultures) there were ceremonies that celebrate adulthood, typically occurring during adolescence. Seijin shiki (literally "adult ceremony") is a Japanese example of this. Upanayanam is a coming of age ceremony for males in the Hindu world. In Judaism, 12-year-old females and 13-year-old males become b'nai mitzvah and often have a celebration to mark this coming of age. Among some denominations of Christianity, the rite or sacrament of Confirmation is received by adolescents and may be considered the time at which adolescents becomes members of the church in their own right. African boys also have a coming of age ceremony in which, upon reaching adolescence, the males state a promise to never do anything to shame their families or their village. This was also continued among African-American slaves in the early days of slavery before the practice was outlawed. In America, girls will often have a "sweet sixteen" party to celebrate turning the aforementioned age, a tradition similar to the quinceañera in Latino culture. Teenagers have also been an important factor in many movements for positive social change around the world. The popular history of adolescents participating in these movements may perhaps start with Joan of Arc, and extend to present times with popular youth activism, student activism, and other efforts to make youth voice heard.

Legal issues

A number of social scientists, including anthropologist Margaret Mead and sociologist Mike Males, have repeatedly noted the contradictory treatment of laws affecting adolescents in the United States. As Males has noted, the US Supreme Court has, "explicitly ruled that policy-makers may impose adult responsibilities and punishments on individual youths as if they were adults at the same time laws and policies abrogate adolescents’ rights en masse as if they were children."

Internationally, those over a certain age (often 18, though this varies) are legally considered responsible adults. Those who are under the age of legal responsibility may be considered too young to be held accountable for criminal action. This is called the defense of infancy.

The issue of youth activism affecting political, social, educational, and moral circumstances is of growing significance around the world. Youth-led organizations around the world have fought for social justice, the youth vote seeking to gain teenagers the right to vote, to secure more youth rights, and demanding better schools through student activism.

Youth are also becoming more involved in community leadership, governance, and service. Volunteerism among youth is at a record high, while student voice in schools and youth voice in communities is being engaged in community organizations, government boards, and in youth-serving nonprofit staffs and leadership.

The sale of selected items such as cigarettes, alcohol, and videos with sexual or violent content is often prohibited based on age. Such age restrictions vary widely. In practice, it is common that young people engage in underage smoking or drinking, and in some cultures this is tolerated to a certain degree. In the United States, teenagers are usually allowed to drive at 16 (each state sets its own minimum driving age of which a curfew may be imposed), but they cannot legally purchase or consume alcohol until 21. In Europe it is more common for the driving age to be higher (18, usually) while the drinking age is lower than that of the US (usually 18 when unaccompanied). The traditional age of full maturity in the U.S. is 21 and, until recently (see: Twenty-sixth amendment) people were not legally allowed to vote until this age. At present, citizens may vote at 18 and usually can run in local and state elections at that age (and sometimes do; in rare cases, high school students have run for school board positions^{[citation needed]}, and at least one has been elected mayor.^[8] One must be 25, however, to serve in the House of Representatives and 30 to serve in the Senate, or 35 to serve as the President of the United States.

Given the emotional immaturity of adolescents, many countries consider those under a certain age to be too young to engage in sexual intercourse and other sexual activities with adults, even if they are physiologically capable (see age of consent). This issue has been most famously dramatized in the book Lolita (and two movies). Pedophilia is defined as interest in children before puberty, yet informally in the United States and other countries, it may also include interest in adolescents, with their maturing bodies (although the correct term for an interest in post-pubescent adolescents is called Ephebophilia). In some other countries or cultures, typically those in which extended family relationships prevent the quick taking-up and dropping of romantic relationships, relationships between adults and adolescents are socially accepted or viewed with tolerance. See pedophilia and ephebophilia for more information. In many countries, sex with adolescents below a certain age has become a social issue and is considered a serious sex crime. The age of consent varies according to the country or state/region. Countries without such laws may be targets for child sex tourism, if their laws do not separate prostitution from normal relationships.

Pornography involving those under a certain age, typically 18 (see child pornography), is also considered unacceptable and strictly prohibited in most countries. Female adolescents are sometimes forced to engage in prostitution and slavery, even at a young age.

Since the advent of the Convention on the Rights of the Child in 1989, almost every country (except the U.S. & Somalia) in the world has become voluntarily legally committed to advancing an anti-discriminatory stance towards young people of all ages. This is a legally binding document which secures youth participation throughout society while acting against unchecked child labor, child soldiers, child prostitution, and pornography.